High/low temperature operation of electric double layer capacitor utilizing acidic cellulose-chitin hybrid gel electrolyte

An acidic cellulose-chitin hybrid gel electrolyte consisting of cellulose, chitin, 1-butyl-3-methylimidazolium, 1-allyl-3-methylimidazolium bromide, and an aqueous H₂SO₄ solution is investigated for electric double layer capacitors (EDLCs) with activated carbon fiber cloth electrodes. The acidic cellulose-chitin hybrid gel electrolyte shows a high ionic conductivity comparable to that for an aqueous 2 mol dm⁻³ H₂SO₄ solution at 0-80 °C. This system's temperature dependence in EDLC performance is investigated by galvanostatic charge-discharge measurement. An EDLC cell with the acidic hybrid gel electrolyte has higher capacitance than that with the aqueous H₂SO₄ solution in the range of operation temperatures (−10 to 60 °C). Moreover, the capacitance retention of the EDLC cell with the acidic hybrid gel electrolyte is better than that of a cell with the H₂SO₄ solution at 60 °C over 10,000 cycles. This suggests that the proposed acidic gel electrolyte has excellent stability in the presence of a strong acid, even at a high temperature of 60 °C.     

Analysis and performance assessment of NH3 and H2 fed SOFC with proton-conducting electrolyte

The present paper investigates the performance of a solid oxide fuel cell based on proton-conducting electrolyte (SOFC-H⁺) using one-dimensional steady-state model. The analysis covers a detailed electro-chemical model for H₂ and NH₃ fuels. The direct internal reforming of NH₃ is examined, and the effects of some operating parameters (e.g. temperature, pressure, fuel utilization and oxidant utilization) on the reversible cell potential are investigated. In addition, the overpotentials (including activation, ohmic and concentration) are calculated to study the irreversible behavior of the SOFC-H⁺ with some actual data operating conditions and material properties taken from the literature. In addition, effects of some operation and structural parameters on cell performance were examined. The present results indicate that the activation and the ohmic losses are considerable. The concentration overpotential at the anode side is negligible due to the fact that H₂O is produced at the cathode side. The maximum power density is calculated as 3212 and 3113 W/m² at 1073 K and 1 atm for the fuels of H₂ and NH₃. The results further show that H₂ provides better performance than NH₃ at the same partial pressure. Moreover, NH₃ is an excellent hydrogen carrier which is a potential candidate for SOFC-H⁺ due to its high hydrogen content and considerable cell performance.     

Quasi-solid state dye-sensitized solar cells based on gel polymer electrolyte with poly(acrylonitrile-co-styrene)/NaI+I2

Gel polymer electrolyte based on poly(acrylonitrile-co-styrene)/NaI+I₂ and binary solvent mixture was prepared. When the system contains 0.5 M NaI and 0.05 M I₂, the maximum ionic conductivity (at 30 °C) of 2.37 mS cm⁻¹ was achieved. Based on a gel polymer electrolyte with 0.5 M NaI, 0.05 M I₂ and 0.5 M 4-tert-butylpyridine, a quasi-solid state dye-sensitized solar cell was fabricated and its overall energy conversion efficiency of light-to-electricity of 2.75% was achieved under irradiation of 60 mW cm⁻².     

Hybrid supercapacitor based on MnO2 and columned FeOOH using Li2SO4 electrolyte solution

The nano-sized columned β-FeOOH was prepared by the hydrolysis process and its electrochemical capacitance performance was evaluated for the first time in Li₂SO₄ solution. A hybrid supercapacitor based on MnO₂ positive electrode and FeOOH negative electrode in Li₂SO₄ electrolyte solution was designed. The electrochemical tests demonstrated that the hybrid supercapacitor has a energy density of 12 Wh kg⁻¹ and a power density of 3700 W kg⁻¹ based on the total weight of the electrode active materials with a voltage range 0–1.85 V. This hybrid supercapacitor also exhibits a good cycling performance and keeps 85% of initial capacity over 2000 cycles.     

Conductive performances of solid polymer electrolyte films based on PVB/LiClO4 plasticized by PEG200, PEG400 and PEG600

Solid polymer electrolyte (SPE) films consisting of polyvinyl butyral (PVB) as host polymer, LiClO₄ as alkali salt at mole ratio of [O]:[Li] = 8, and different molecular weight polyethylene glycol (PEG) including PEG₂₀₀, PEG₄₀₀, and PEG₆₀₀ as plasticizers are prepared by physical blending method. The dielectric relaxation and electrochemical impedance measurements reveal that the conductive performances are improved by adding PEG as plasticizers through the enhancement in the moving space for ions, and PEG₄₀₀ performs plasticizing effect superior to PEG₂₀₀ and PEG₆₀₀. Their conductivity is measured by using a sandwiched Pt/SPE/Pt cell model. SPE with 30% PEG₄₀₀ (wt%) of PVB exhibits the maximum conductivity at room temperature, and its conductivity increases linearly with temperatures from 303 to 333 K at two to three orders of magnitude higher than that of the other two SPEs containing 30% PEG₂₀₀ and 30% PEG₆₀₀, respectively. However, their conductivity does not increase linearly with the increase in heating temperatures until the temperature reaches around 333 K; the decrease in conductivity with heating from their maxima is attributed to the restriction of ion moving space because of the crosslinking reaction between hydroxyl and aldehyde groups. As observed from the XRD and the microscopy results, PEG₄₀₀ is more effective than others in enhancing the conductive performances of these SPEs through changing LiClO₄ from crystalline to amorphous state, increasing the flexibility of PVB, disturbing the short distance sequential order of PVB chains, and promoting the formation of ‘pathway’ for ions’ movement.     

Polypropylene-supported and nano-Al2O3 doped poly(ethylene oxide)-poly(vinylidene fluoride-hexafluoropropylene)-based gel electrolyte for lithium ion batteries

A new gel polymer electrolyte (GPE) is reported in this paper. In this GPE, blending polymer of poly(ethylene oxide) (PEO) with poly(vinylidene fluoride-hexafluoropropylene) (P(VdF-HFP)), doped with nano-Al₂O₃ and supported by polypropylene (PP), is used as polymer matrix, namely PEO-P(VdF-HFP)-Al₂O₃/PP. The performances of the PEO-P(VdF-HFP)-Al₂O₃/PP membrane and the corresponding GPE are characterized with mechanical test, CA, EIS, TGA and charge-discharge test. It is found that the performances of the membrane and the GPE depend to a great extent on the content of doped nano-Al₂O₃. With doping 10 wt.% nano-Al₂O₃ in PEO-P(VdF-HFP), the mechanical strength from 9.3 MPa to 14.3 MPa, the porosity of the membrane increases from 42% to 49%, the electrolyte uptake from 176% to 273%, the thermal decomposition temperature from 225 °C to 355 °C, and the ionic conductivity of corresponding GPE is improved from 2.7 × 10⁻³ S cm⁻¹ to 3.8 × 10⁻³ S cm⁻¹. The lithium ion battery using this GPE exhibits good rate and cycle performances.     

Preparation and electrochemical characterization of gel polymer electrolyte based on electrospun polyacrylonitrile nonwoven membranes for lithium batteries

Electrospun membranes of polyacrylonitrile are prepared, and the electrospinning parameters are optimized to get fibrous membranes with uniform bead-free morphology. The polymer solution of 16 wt.% in N,N-dimethylformamide at an applied voltage of 20 kV results in the nanofibrous membrane with average fiber diameter of 350 nm and narrow fiber diameter distribution. Gel polymer electrolytes are prepared by activating the nonwoven membranes with different liquid electrolytes. The nanometer level fiber diameter and fully interconnected pore structure of the host polymer membranes facilitate easy penetration of the liquid electrolyte. The gel polymer electrolytes show high electrolyte uptake (>390%) and high ionic conductivity (>2 × 10⁻³ S cm⁻¹). The cell fabricated with the gel polymer electrolytes shows good interfacial stability and oxidation stability >4.7 V. Prototype coin cells with gel polymer electrolytes based on a membrane activated with 1 M LiPF₆ in ethylene carbonate/dimethyl carbonate or propylene carbonate are evaluated for discharge capacity and cycle property in Li/LiFePO₄ cells at room temperature. The cells show remarkably good cycle performance with high initial discharge properties and low capacity fade under continuous cycling.     

New composite polymer electrolyte comprising mesoporous lithium aluminate nanosheets and PEO/LiClO4

Mesoporous materials, due to its potential for advanced applications in catalysis and nanoscience, have attracted much attention in the past decade. In this work, mesoporous lithium aluminate (next called MLA) nanosheets with high specific surface area were prepared by a hydrothermal method using hex-adecyltrimethyl ammonium bromide (CTAB) as the template. A novel PEO-based composite polymer electrolyte has been developed by using MLA powders as the filler. The electrochemical impedance showed that the conductivity was improved simultaneously. A high conductivity of 2.24 × 10⁻⁵ S cm⁻¹ at 25 °C was obtained. The lithium polymer battery using this novel composite polymer electrolyte and with lithium metal and LiFePO₄ employed as anode and cathode, respectively, showed high discharge capacity (more than 140 mAh g⁻¹ at 60 °C) and excellent cycling stability as revealed by galvanostastically charge/discharge cycling tests. The excellent electrochemical performances at low temperature of the cells were obtained, which was attributed to the high surface area and channels structure of the filler. The excellent properties of the solid-state lithium battery suggested that, PEO₁₆–LiClO₄–MLA composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

Low temperature synthesis of Yb doped SrCeO3 powders by gel combustion process

In this work, SrCe_0.9Yb_0.1O_3−δ powders were synthesized by a gel combustion method which combined gel process and combustion process. The effect of ratio of citric acid to metal cations (C/M), oxidizer and calcination temperature on the properties of powders was investigated in detail. It was found that the extra oxidizer NH₄NO₃ increased the flame temperature of combustion and thus promoted the formation of SrCeO₃. The relative amount of SrCeO₃ in powder increased as the C/M ratio increased. The as-ignited powder at 250 °C mainly consisted of the perovskite SrCeO₃, i.e. relative amount of 95.2 wt%. The adiabatic flame temperature of the combustion reaction was calculated to be 1903.1 °C, higher than the required formation temperature of 787.2 °C for SrCeO₃. Furthermore, the pure perovskite phase powder with agglomerated microstructure and average grain size of 2 μm was obtained after calcination at 1200 °C for 5 h. This heat-treatment temperature is 200 °C lower than the conventional solid state reaction method for SrCe_0.9Yb_0.1O_3−δ preparation.     

Performance improvement of polyethylene-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate based gel polymer electrolyte by doping nano-Al2O3

Polyethylene (PE)-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate with and without doping nano-Al₂O₃, namely P(MMA-VAc)-co-PEGDA/PE and P(MMA-VAc)-co-PEGDA/Al₂O₃/PE, are prepared and their performances as gel polymer electrolytes (GPEs) for lithium ion battery are studied by mechanical test, scanning electron microscopy, thermogravimetric analyzer, electrochemical impedance spectroscopy, cyclic voltammetry, and charge/discharge test. It is found that the doping of nano-Al₂O₃ in the P(MMA-VAc)-co-PEGDA/PE improves the comprehensive performances of the GPE and thus the rate performance and cyclic stability of the battery. With doping nano-Al₂O₃, the mechanical and thermal stability of the polymer and the ionic conductivity of the corresponding GPE increases slightly, while the battery exhibits better cyclic stability. The mechanical strength and the decomposition temperature of the polymer increase from 15.9 MPa to 16.2 MPa and from 410 °C to 420 °C, respectively. The ionic conductivity of the GPE is from 3.4 × 10⁻³ S cm⁻¹ to 3.8 × 10⁻³ S cm⁻¹. The discharge capacity of the battery using the GPE with doping nano-Al₂O₃ keeps 90.9% of its initial capacity after 100 cycles and shows good C-rate performance.     

Proton conductivity and chemical stability of Li2SO4 based electrolyte in a H2S–air fuel cell

Proton conductivity of Li₂SO₄-Al₂O₃ (LA) based electrolyte was determined under non-reducing dynamic conditions using current interruption technique. The performance of LA as electrolyte has been examined at 600 °C in a H₂S fuel cell with MoS₂-NiS as anode catalyst and NiO as cathode catalyst. XRD and XPS results show that Li₂SO₄ is not stable when heated in pure H₂S as it is reduced to Li₂S by hydrogen produced in equilibrium amounts from the thermal decomposition of H₂S. In contrast, under dynamic operation in a H₂S fuel cell the concentration of H₂ is much lower, the reduction reaction does not occur and, surprisingly, Li₂SO₄ is a chemically stable electrolyte.     

Interfacial properties between LiFePO4 and poly(ethylene oxide)-Li(CF3SO2)2N polymer electrolyte

The interface resistance between Li_xFePO₄ and poly(ethylene oxide) (PEO)-Li(CF₃SO₂)₂N (LiTFSI) was examined by AC impedance measurement of a Li_xFePO₄/PEO-LiTFSI/Li_xFePO₄ cell in the temperature range of 30-60 °C. Four types of resistance, R0, R1, R2 and R3 were proposed according to analysis of the cell impedance using an equivalent circuit. The sum of R0 and R1 in the high frequency range is consistent with the resistance of the PEO electrolyte. R2 in the middle frequency range is related to lithium ion transport to an active point for charge transfer inside the composite electrode, and R3 in the low frequency range is considered to be the charge transfer resistance. The activation energy for R2 was affected by the thickness and composition of the electrode, whereas that for R3 was not.     

A polymer gel electrolyte composed of a poly(ethylene oxide) copolymer and the influence of its composition on the dynamics and performance of dye-sensitized solar cells

A polymer gel electrolyte composed of a poly(ethylene oxide) derivative, poly(ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether), mixed with gamma-butyrolactone (GBL), LiI and I₂ is employed in dye sensitized solar cells (DSSC). The electrolyte is characterized by conductivity experiments, Raman spectroscopy and thermal analysis. The influence of the electrolyte composition on the kinetics of DSSC is also investigated by transient absorption spectroscopy (TAS). The electrolyte containing 70 wt.% of GBL and 20 wt.% of LiI presents the highest conductivity (1.9 × 10⁻³ S cm⁻¹). An efficiency of 4.4% is achieved using this composition. The increase in I_SC as a function of GBL can be attributed an increase in the mobility of the iodide (polyiodide) species. The increase in the yield of the intermediate species, I₂⁻, originating in the regeneration reaction, is confirmed by TAS. However, the charge recombination process is faster at this composition and a decrease in the V_oc is observed. Photovoltage decay experiments confirm an acceleration in charge recombination for the DSSC assembled with the electrolyte containing more GBL. Raman investigations show that in this electrolyte the I₅⁻/I₃⁻ ratio is higher. Theoretical calculations also indicate that the I₅⁻ species is a better electron acceptor.     

Influence of H2SO4 concentration on the performance of lead-acid battery negative plates

The influence of sulfuric acid concentration on negative plate performance has been studied on 12 V/32 Ah lead-acid batteries with three negative and four positive plates per cell, i.e. the negative active material limits battery capacity. Initial capacity tests, including C20 capacity, cold cranking ability and Peukert tests, have been carried out in a wide range of sulfuric acid concentrations (from 1.18 to 1.33 sp.gr.). High initial capacity and good CCA performance were registered for batteries with acid concentration between 1.24 and 1.30 sp.gr. The charge acceptance depends on acid concentration as well as on battery state of charge. Batteries with high SoC exhibit high charge acceptance at low acid concentrations. The cycle life tests at two discharge rates (10 and 3 h discharge) evidence that sulfuric acid concentration exerts a strong effect on negative plate performance. The cycle life of batteries decreases with increase of acid concentration. The obtained results demonstrate the high impact of lead sulfate solubility on the cycle life and charge efficiency of lead-acid batteries.     

Electrochemical performance of all-solid-state Li batteries based LiMn0.5Ni0.5O2 cathode and NASICON-type electrolyte

LiNi_0.5Mn_0.5O₂ thin films have been deposited on the NASICON-type glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering followed by annealing. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. All-solid-state Li/PEO₁₈-Li(CF₃SO₂)₂N/LATSP/LiNi_0.5Mn_0.5O₂/Au cells are fabricated using the LiNi_0.5Mn_0.5O₂ thin films and the LATSP electrolyte. The electrochemical performance of the cells is investigated by galvanostatic cycling, cyclic voltammetry (CV), potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS). Interfacial reactions between LiNi_0.5Mn_0.5O₂ and LATSP occur at a temperature as low as 300 °C with the formation of Mn₃O₄, resulting in an increased obstacle for Li-ion diffusion across the LiNi_0.5Mn_0.5O₂/LATSP interface. The electrochemical performance of the cells is limited by the interfacial resistance between LATSP and LiNi_0.5Mn_0.5O₂ as well as the Li-ion diffusion kinetics in LiNi_0.5Mn_0.5O₂ bulk.     

A thermodynamic analysis of the SO2/H2SO4 system in SO2-depolarized electrolysis

The hybrid sulfur thermochemical cycle has been proposed as a means to produce efficiently massive quantities of clean hydrogen using a high-temperature heat source like nuclear or solar. The cycle consists of two steps, one of which is electrolytic. The reversible cell potential for this step and, hence, the resulting operating potential will depend on the concentrations of dissolved SO₂ and sulfuric acid at the electrode. To understand better how these are related as functions of temperature and pressure, an Aspen Plus phase equilibrium model using the OLI Mixed Solvent Electrolyte physical properties method was employed to determine the activities of the species present in the system. These activities were used in conjunction with the Nernst equation to determine the reversible cell potential as a function of sulfuric acid concentration, temperature and pressure. A significant difference between the reversible and actual cell potentials was found, suggesting that there may be considerable room for reducing the operating potential.     

Electrochemical profile of an asymmetric supercapacitor using carbon-coated LiTi2(PO4)3 and active carbon electrodes

In this work, we reported an asymmetric supercapacitor in which active carbon (AC) was used as a positive electrode and carbon-coated LiTi₂(PO₄)₃ as a negative electrode in 1 M Li₂SO₄ aqueous electrolyte. The LiTi₂(PO₄)₃/AC hybrid supercapacitor showed a sloping voltage profile from 0.3 to 1.5 V, at an average voltage near 0.9 V, and delivered a capacity of 30 mAh g⁻¹ and an energy density of 27 Wh kg⁻¹ based on the total weight of the active electrode materials. It exhibited a desirable profile and maintained over 85% of its initial energy density after 1000 cycles. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1000 W kg⁻¹, it had a specific energy 15 Wh kg⁻¹ compared with 24 Wh kg⁻¹ at the power density about 200 W kg⁻¹.     

Industrial scale modelling of the thermochemical energy storage system based on CO2 + 2NH3 ↔ NH2COONH4 equilibrium

The thermochemical storage of energy by the system carbon dioxide, ammonia and ammonium carbamate is studied in detail. In particular, the kinetics and the thermodynamics of the reversible reaction is studied. We give two industrial models for the operation of this system. In the first, the separation of the gases NH₃ and CO₂ is achieved by compression and liquefaction of NH₃. In the second, a method of separation of the gases is proposed which is based on the solubility of NH₃ in ethanol while CO₂ is practically insoluble. The operation of this system is examined both in closed form and in the case in which CO₂ is rejected in the atmosphere, and it is taken from alcoholic fermentation or from the combustion gases of power plants burning lignite. The mass and energy balance is given, for each case, and the amount of energy losses by the use of this storage system is calculated. Finally, we give some estimates for the area of solar collectors and the amount of chemicals which are required in order to cover the energy needs of a community.